A method and application for constructing hierarchical porous carbon material by using low-melting-point eutectic salt in cooperation with a biological template
By synergistically constructing hierarchical porous carbon materials with low-melting-point eutectic salts and biological templates, the problems of equipment corrosion and environmental pollution in the preparation of high specific surface area activated carbon have been solved, and the preparation of high-performance supercapacitor electrode materials has been realized, which have environmental protection, energy saving and high rate performance.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- HUANENG CHONGQING LUOWEN POWER CO LTD
- Filing Date
- 2026-04-03
- Publication Date
- 2026-06-09
AI Technical Summary
Existing methods for preparing high specific surface area activated carbon suffer from problems such as strong equipment corrosion, serious environmental pollution, weak mesopore control, and resource waste, leading to rapid performance degradation of supercapacitors at high current densities.
By employing the synergistic effect of low-melting-point eutectic salt and biological template, biomass and eutectic salt are mixed through physical mixing or liquid-phase impregnation. After high-temperature pyrolysis, inorganic salts are washed and recovered to prepare hierarchical porous carbon materials. The liquid-phase pore-forming template of eutectic salt and reaction medium are used to construct a micropore-mesopore-macropore interconnected structure.
We have achieved the preparation of hierarchical porous carbon materials with high specific surface area and environmental protection and energy saving. These materials have excellent electrochemical and rate performance and are suitable for applications such as supercapacitor electrodes. This method solves the problems of environmental pollution and structural control associated with traditional methods.
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Abstract
Description
Technical Field
[0001] This disclosure belongs to the field of nanoporous material preparation and energy storage technology, specifically relating to a method and application of constructing hierarchical porous carbon materials using low-melting-point eutectic salts in conjunction with biological templates. Background Technology
[0002] Supercapacitors, as a new type of energy storage device between traditional capacitors and secondary batteries, have significant advantages such as high power density, fast charging and discharging speed, long cycle life, and wide operating temperature range. They are widely used in urban public transport electrification, rail transit energy recovery, power grid frequency regulation, and portable electronic devices.
[0003] Porous carbon materials are the most mainstream electrode materials for supercapacitors. Their charge storage primarily relies on the electrical double layer capacity formed at the interface between the electrode surface and the electrolyte. Therefore, the specific surface area (SSA), pore size distribution (PSD), and channel connectivity of the electrode material directly determine the specific capacitance and rate performance of the capacitor. Ideally, porous carbon materials for supercapacitors should possess the following structural characteristics: (1) High specific surface area micropores (<2 nm): provide a large number of charge storage sites; (2) Appropriate amount of mesopores (2-50 nm): serve as fast channels for ion transport and reduce ion diffusion resistance; (3) A certain amount of macropores (>50 nm): serve as "reservoirs" for electrolytes and shorten the diffusion path of ions into micropores. This hierarchical pore structure with interconnected micropores, mesopores and macropores is recognized as the optimal solution for obtaining high-performance electric double-layer capacitors.
[0004] In current industrial production, high specific surface area activated carbon is mostly prepared using the KOH chemical activation method. Although KOH activation can achieve extremely high specific surface areas (>2000 m²), 2 However, this process has serious drawbacks: First, KOH is extremely corrosive, causing severe damage to stainless steel and other reaction vessel equipment at high temperatures, significantly increasing maintenance costs; second, the activation process generates a large amount of acid and alkaline wastewater, putting enormous pressure on environmental treatment; third, KOH activation tends to generate a large number of micropores, while the ability to control mesopores is weak, leading to rapid performance degradation under high current density; fourth, KOH cannot be recycled and reused. Summary of the Invention
[0005] This disclosure aims to at least solve one of the technical problems existing in the prior art, and to provide a method and application for constructing hierarchical porous carbon materials using low-melting-point eutectic salts in conjunction with bio-templates.
[0006] One aspect of this disclosure provides a method for constructing hierarchical porous carbon materials using low-melting-point eutectic salts in conjunction with biotemplates, the method comprising: Lignocellulosic biomass raw materials with vascular or pore structures are selected, and biomass powder is obtained after crushing, washing, and drying. At least two alkali metal halides are mixed in a eutectic ratio and ground to obtain a low-melting-point eutectic salt mixture; The biomass powder and the eutectic salt mixture are physically mixed or liquid-phase impregnated and then dried to obtain an inorganic salt / biomass composite precursor. The inorganic salt / biomass composite precursor was pyrolyzed in a high-temperature reactor under an inert atmosphere. During the pyrolysis process, the eutectic salt was in a molten state and served as a liquid-phase pore-forming template and reaction medium to obtain the reaction product. After the reaction product is cooled to room temperature, it is placed in deionized water and stirred to wash, dissolve and separate the inorganic salts therein, and the washing liquid is evaporated and crystallized to obtain a solid product; The washed solid product was soaked in dilute acid, washed with water until neutral, dried and sieved to obtain the hierarchical porous carbon material.
[0007] Optionally, the lignocellulosic biomass raw material is selected from one or more of bamboo, cotton stalks, hemp fiber, sugarcane bagasse, corn cobs, and sawdust.
[0008] Optionally, the eutectic salt mixture is one of NaCl-KCl, LiCl-KCl, LiCl-NaCl-KCl, LiCl-LiBr, and NaCl-Na2CO3; The melting point of the eutectic salt mixture is below 700°C.
[0009] Optionally, the mass ratio of the biomass powder to the eutectic salt mixture is 1:(2-10), and the drying temperature is 60℃-120℃.
[0010] Optionally, the pyrolysis treatment temperature is 700℃-950℃, the heating rate is 3-10℃ / min, and the holding time is 2-8h.
[0011] Optionally, the dilute acid soaking uses hydrochloric acid with a concentration of 0.5-2.0 mol / L.
[0012] Optionally, the hierarchical porous carbon material has a three-level hierarchical structure of micropores, mesopores, and macropores, with a specific surface area of 1500 to 2600 m². 2 / g, with a total pore volume of 0.8 to 1.6 cm³. 3 / g, with mesoporous components accounting for 30% to 55%.
[0013] In another aspect of this disclosure, a hierarchical porous carbon material is provided, which is prepared by the method described above.
[0014] In another aspect of this disclosure, an application of a hierarchical porous carbon material is proposed, which is used in supercapacitor electrodes, electrodeionization, heavy metal ion adsorption, or catalyst supports.
[0015] Optionally, the hierarchical porous carbon material has a specific capacity greater than 320 F / g in a three-electrode system and 6 mol / L KOH electrolyte at a current density of 0.5 A / g, and a capacity retention rate greater than 80% at a high current density of 20 A / g.
[0016] This disclosure presents a method for preparing hierarchical porous carbon materials using eutectic salts in conjunction with biological templates, along with the hierarchical porous carbon materials and their applications. This method successfully solves the pollution and structure control challenges in the preparation of high specific surface area carbon materials. The prepared carbon materials exhibit excellent energy storage properties, making them particularly suitable as electrode materials for high-power supercapacitors. This method features a mature process route, high salt recovery rate, and wide adaptability to raw materials, providing significant reference value for promoting the large-scale production of green energy storage materials. Attached Figure Description
[0017] Figure 1 This is a flowchart illustrating a specific embodiment of the method for constructing hierarchical porous carbon materials using low-melting-point eutectic salts in conjunction with bio-templates. Detailed Implementation
[0018] To enable those skilled in the art to better understand the technical solutions of this disclosure, the disclosure will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain this disclosure and represent a part of the embodiments of this disclosure, not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this disclosure without creative effort are within the protection scope of this disclosure.
[0019] As shown in Figure 1, one aspect of this disclosure provides a method S100 for constructing hierarchical porous carbon materials using low-melting-point eutectic salts in conjunction with bio-templates, specifically including the following steps S110~S160: S110. Biomass precursor pretreatment: Select lignocellulosic biomass raw materials with vascular or pore structures, and obtain biomass powder after crushing, washing and drying.
[0020] In step S110, the lignocellulosic biomass raw material is selected from one or more of bamboo, cotton stalks, hemp fiber, sugarcane bagasse, corn cob, and sawdust. The above raw materials are common biological materials with low cost.
[0021] In step S110, the biomass raw material is crushed to 60-100 mesh, washed with 2% dilute hydrochloric acid to remove natural mineral impurities such as calcium and magnesium, and then dried for later use.
[0022] It should be noted that biomass, as a carbon source with vast reserves and a natural hierarchical structure, can naturally form macropores or mesopores by utilizing its own water-carrying channels (such as xylem vessels) as templates. Based on this, this embodiment organically combines the macroscopic channels of biomass with microscopic pore-forming technology.
[0023] S120, Construction of eutectic salt system: Mix at least two alkali metal halides in a eutectic ratio and grind to obtain a low-melting-point eutectic salt mixture.
[0024] In step S120, the eutectic salt mixture is selected from one of NaCl-KCl, LiCl-KCl, LiCl-NaCl-KCl, LiCl-LiBr, and NaCl-Na2CO3. Simultaneously, the melting point of the eutectic salt mixture is below 700℃.
[0025] As a further preferred option, the eutectic salt mixture is preferably a NaCl-KCl mixture with a molar ratio of approximately 657°C.
[0026] As a further preferred option, the eutectic salt mixture is preferably a LiCl-KCl mixture with a mass ratio of 45:55 and a melting point of about 353°C.
[0027] S130. Composite impregnation and mixing: The biomass powder and the eutectic salt mixture are physically mixed or liquid-phase impregnated and mixed, and then dried to obtain an inorganic salt / biomass composite precursor.
[0028] In step S130, the mass ratio of biomass powder to the eutectic salt mixture is 1:(2-10), for example, preferably 1:(3-6), and the drying temperature is 60℃-120℃, for example, preferably 800-900℃. This temperature range ensures that the salt is in a low-viscosity liquid state, which can fully wet the carbonaceous intermediates produced by biomass pyrolysis.
[0029] S140, Eutectic Salt Medium Pyrolysis: The inorganic salt / biomass composite precursor is placed in a high-temperature reactor under an inert atmosphere for pyrolysis treatment. During the pyrolysis process, the eutectic salt is in a molten state and serves as a liquid phase pore-forming template and reaction medium to obtain the reaction product.
[0030] In step S140, the pyrolysis temperature is 700℃-950℃, the heating rate is 3-10℃ / min, and the holding time is 2-8h.
[0031] It should be further noted that, compared to KOH activation, the molten salt method, as an emerging synthesis technique, utilizes the stability and site-occupancy effect of liquid-phase inorganic salts at high temperatures to achieve mild pore formation in carbon materials. It offers advantages such as low corrosivity, salt recyclability, and environmental friendliness. However, single inorganic salts (such as NaCl) have high melting points and slow reaction kinetics. Therefore, this disclosure employs a eutectic salt system, which can significantly reduce the reaction temperature. By adjusting the type and mixing ratio of salts, precise control over the pore structure of carbon materials can be achieved.
[0032] S150 Washing and Salt Recovery: After the reaction product is cooled to room temperature, it is placed in deionized water and stirred to wash, dissolve and separate the inorganic salts therein, and the washing liquid is evaporated and crystallized to realize the recycling of eutectic salt.
[0033] In step S150, deionized water is preferably hot water, so that inorganic salts can be dissolved quickly. Carbon material is obtained by filtration, and more than 95% of the eutectic salt can be recovered by evaporation and crystallization of the filtrate.
[0034] S160. Refining process: The washed solid product is soaked in dilute acid, washed with water until neutral, dried and sieved to obtain the graded porous carbon material.
[0035] In step S160, the dilute acid immersion uses hydrochloric acid with a concentration of 0.5-2.0 mol / L, which aims to remove the inherent metallic minerals in the biomass.
[0036] The hierarchical porous carbon material of this embodiment has a three-level hierarchical structure of micropores, mesopores, and macropores, with a specific surface area of 1500 to 2600 m². 2 / g, with a total pore volume of 0.8 to 1.6 cm³. 3 / g, with mesoporous components accounting for 30% to 55%.
[0037] The technical principles of this disclosure are as follows: This invention uses natural biomass (such as bamboo fiber, sugarcane bagasse, etc.) as a precursor, which has highly oriented anisotropic vessels. When the biomass is mixed with a eutectic salt and heated above its melting point, the molten liquid salt rapidly penetrates into the cell walls and natural channels of the biomass through capillary pressure.
[0038] In addition, the liquid-phase salt plays multiple roles during pyrolysis: 1. Dehydration-assisted catalysis: Molten salt, as a Lewis acid-base system, can induce dehydration and decarboxylation reactions in biomass components at lower temperatures, thereby increasing carbon yield.
[0039] 2. Site template function: At high temperatures, the salts are distributed in a liquid state between the carbon layers, preventing severe collapse of the carbon skeleton. Upon cooling, these salts recrystallize within the carbon.
[0040] 3. Stripping and etching: Cations in molten salt (such as Li) + Na + , K + At high temperatures, it will embed between carbon layers, which will act as a means of peeling off carbon sheets, thereby creating a large number of micropores.
[0041] 4. Structural Preservation: The original large-sized vessels of biomass are preserved during carbonization because they are filled with liquid salt, eventually forming interconnected hierarchical channels.
[0042] This disclosure achieves efficient and green preparation of hierarchical porous carbon materials through the synergistic effect of eutectic salts and biological templates, exhibiting high specific surface area, excellent electrochemical performance, and environmentally friendly characteristics. The method first selects lignocellulosic biomass with a natural vascular bundle structure as a precursor, mixing it with low-melting-point eutectic inorganic salts (such as NaCl, KCl, LiCl, and combinations thereof) in a specific ratio. Under high-temperature conditions (700℃-900℃), the inorganic salts melt to form a liquid phase medium. Utilizing the occupancy effect, dehydration effect, and exfoliation effect of the liquid-phase salts on biological components, combined with the original vascular structure of the biomass, a hierarchical porous network consisting of interconnected micropores, mesopores, and macropores is constructed in situ. After the reaction, the molten salt can be completely recovered and reused through simple water washing.
[0043] In another aspect of this disclosure, a hierarchical porous carbon material is proposed, which is prepared by the method described above.
[0044] The porous carbon material prepared in this disclosure has a high specific surface area (1500-2600 m²). 2 / g), with well-developed porosity and anisotropic ion transport channels.
[0045] In another aspect of this disclosure, an application of a hierarchical porous carbon material is proposed, which is used in supercapacitor electrodes, electrodeionization, heavy metal ion adsorption, or catalyst supports.
[0046] In some preferred embodiments, hierarchical porous carbon materials are preferably used in sulfur-supported substrates for lithium-sulfur batteries or in the anodes of sodium-ion batteries.
[0047] As a further preferred option, the hierarchical porous carbon material in a three-electrode system, in a 6 mol / L KOH electrolyte, has a specific capacity greater than 320 F / g at a current density of 0.5 A / g, and a capacity retention rate greater than 80% at a high current density of 20 A / g.
[0048] In electrochemical tests, the material exhibits extremely high specific capacity (greater than 320 F / g at 0.5 A / g) and excellent rate performance. Moreover, the preparation process generates no corrosive waste liquid, demonstrating significant environmental advantages and industrial application potential.
[0049] The following will further illustrate the method and application of constructing hierarchical porous carbon materials using low-melting-point eutectic salts in conjunction with biotemplates, with specific examples: Example 1 This example demonstrates the preparation of bamboo-based hierarchical porous carbon materials using NaCl-KCl eutectic salts. (1) Take 20g of bamboo fiber powder.
[0050] (2) Prepare 100g of NaCl-KCl eutectic salt with an equimolar ratio (mass ratio of approximately 44:56), and mix the biomass and salt in a planetary ball mill for 30 minutes.
[0051] (3) Place the mixture in a tube furnace and heat it to 850°C at 5°C / min under nitrogen protection, and keep it at that temperature for 4 hours.
[0052] (4) After cooling, place the black solid in deionized water at 90℃ and stir. After filtration, evaporate the filtrate to crystallize and recover the salt; wash the filter cake with 0.5 mol / L hydrochloric acid.
[0053] (5) After drying, bamboo-based graded porous carbon (BPC-850) is obtained.
[0054] Test results: The material has a BET specific surface area of 2150 m². 2 / g, total pore volume is 1.28 cm³ 3 / g. The pore size distribution curves show obvious characteristic peaks at 1.2 nm, 3.5 nm and 120 nm, exhibiting a typical hierarchical pore distribution.
[0055] Electrochemical testing: In 6 M KOH electrolyte, the specific capacity was 328 F / g at a current density of 0.5 A / g. When the current density was increased to 20 A / g, the specific capacity remained at 275 F / g (retention rate 83.8%). After 10,000 cycles, the capacity retention rate was 97.2%.
[0056] Example 2 This example demonstrates the preparation of straw-based porous carbon materials using LiCl-KCl eutectic salts: (1) Take 50g of corn stalk powder and 250g of LiCl-KCl eutectic salt (mass ratio 45:55).
[0057] (2) React at 800℃ for 3 hours.
[0058] (3) The post-processing steps are the same as in Example 1.
[0059] Test results: Specific surface area is 1860 m² 2 / g. Tested in 1.0 M H₂SO₄ electrolyte, the specific capacity at 1.0 A / g is 295 F / g. Due to the stronger induction of mesopores by the LiCl system, the mesopore ratio of this material is as high as 48%. It exhibits extremely low equivalent series resistance (ESR) at high currents.
[0060] Example 3 This example illustrates the effect of different salt / material ratios on pore structure: (1) Set the salt / substance ratio to be 2:1, 4:1, and 8:1 respectively.
[0061] (2) The reaction was carried out at 850°C using the method of Example 1.
[0062] Experiments showed that as the salt concentration increased, the specific surface area decreased from 1100 m² / m³. 2 / g increased to 2450 m 2 / g, but the carbon yield decreased from 28% to 16%. This indicates that the salt / material ratio can serve as a key lever for adjusting the balance between capacity and yield. Furthermore, the material prepared under a salt / material ratio of 8:1 exhibits excellent performance in non-aqueous electrolytes (organic systems), with an operating voltage of up to 2.7V and a significantly improved energy density.
[0063] Comparative Example 1 This example demonstrates the traditional KOH activation method (using the same raw materials): (1) Take 20g of the same bamboo fiber and mix them according to KOH / C=3:1.
[0064] (2) Activate at 800℃ for 2 hours.
[0065] Test results: Although the specific surface area reached 2650 m² 2 / g, but the pores are almost all micropores below 1.0 nm.
[0066] Electrolysis test: The specific capacity was 310 F / g at 0.5 A / g, but when the current density increased to 20 A / g, the capacity rapidly decreased to 120 F / g (retention rate of only 38.7%). Furthermore, the stainless steel nickel boat was severely damaged during the experiment, resulting in a large volume of acidic waste liquid requiring treatment.
[0067] The results of the above embodiments show that by selecting different eutectic salt systems (such as NaCl-KCl or LiCl-KCl) and adjusting the salt / biomass ratio, the specific surface area, pore volume and mesopore ratio of the product can be effectively controlled to meet the needs of different application scenarios.
[0068] As can be seen from the results of the above embodiments and comparative examples, although the molten eutectic salt method used in this disclosure is similar to KOH in terms of pore-forming efficiency, it has significant advantages in structural control. Compared with the pure microporous structure produced by the traditional KOH activation method (Comparative Example 1), this disclosure successfully constructs a hierarchical pore network of interconnected micropores, mesopores and macropores through eutectic salt and biological template. That is, eutectic salt can not only create high-density micropores, but more importantly, it can utilize the liquid phase environment to retain the natural channels of biomass and construct an efficient "ion highway (mesopores / macropores)".
[0069] Furthermore, at the same current density (0.5 A / g), the specific capacity of Example 1 of the present invention (328 F / g) is higher than that of Comparative Example 1 (310 F / g). Example 1 has a capacity retention rate of up to 83.8% at 20 A / g, while that of Comparative Example 1 drops sharply to 38.7%, which fully demonstrates the key role of hierarchical pore structure in rapid charge and discharge. The pure microporous carbon in the comparative example lacks this hierarchical structure, and the ions are "blocked" during rapid charge and discharge, resulting in extremely poor rate performance.
[0070] In summary, this disclosure completely surpasses existing strong alkali activation technologies in terms of process economy and environmental friendliness.
[0071] This disclosure proposes a method and application for constructing hierarchical porous carbon materials using low-melting-point eutectic salts in conjunction with bio-templates, which has the following advantages compared to existing technologies: 1. Environmentally friendly and energy-saving: The eutectic salt system is non-corrosive and does not damage equipment. Furthermore, the recycling of salt greatly reduces production costs and environmental impact.
[0072] 2. Hierarchical pore construction: The prepared material has a high specific surface area of over 1500 m2 / g and a controllable mesoporous ratio (20%-50%), effectively solving the problem of limited performance of pure microporous carbon materials under high power.
[0073] 3. Excellent rate performance: Based on the macroporous channels preserved by the bio-template, the diffusion path of electrolyte ions inside the electrode is shortened, and a high specific capacity can still be maintained at an extremely high current density of 50 A / g.
[0074] 4. High applicability: This process is applicable to almost all lignocellulosic biomass and can transform inexpensive agricultural waste into high-value-added energy storage materials.
[0075] It is understood that the above embodiments are merely exemplary embodiments used to illustrate the principles of this disclosure, and this disclosure is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and substance of this disclosure, and these modifications and improvements are also considered to be within the scope of protection of this disclosure.
Claims
1. A method for constructing hierarchical porous carbon materials using low-melting-point eutectic salts in conjunction with bio-templates, characterized in that, The method includes: Lignocellulosic biomass raw materials with vascular or pore structures are selected, and biomass powder is obtained after crushing, washing, and drying. At least two alkali metal halides are mixed in a eutectic ratio and ground to obtain a low-melting-point eutectic salt mixture; The biomass powder and the eutectic salt mixture are physically mixed or liquid-phase impregnated and then dried to obtain an inorganic salt / biomass composite precursor. The inorganic salt / biomass composite precursor was pyrolyzed in a high-temperature reactor under an inert atmosphere to obtain the reaction product. After the reaction product is cooled to room temperature, it is placed in deionized water and stirred to wash, dissolve and separate the inorganic salts therein, and the washing liquid is evaporated and crystallized to obtain a solid product; The washed solid product was soaked in dilute acid, washed with water until neutral, dried and sieved to obtain the hierarchical porous carbon material.
2. The method according to claim 1, characterized in that, The lignocellulosic biomass raw materials are selected from one or more of bamboo, cotton stalks, hemp fiber, sugarcane bagasse, corn cobs, and sawdust.
3. The method according to claim 1, characterized in that, The eutectic salt mixture is one of NaCl-KCl, LiCl-KCl, LiCl-NaCl-KCl, LiCl-LiBr, and NaCl-Na2CO3; The melting point of the eutectic salt mixture is below 700°C.
4. The method according to claim 1, characterized in that, The mass ratio of the biomass powder to the eutectic salt mixture is 1:(2-10), and the drying temperature is 60℃-120℃.
5. The method according to claim 1, characterized in that, The pyrolysis treatment is carried out at a temperature of 700℃-950℃, a heating rate of 3-10℃ / min, and a holding time of 2-8h.
6. The method according to claim 1, characterized in that, The dilute acid soaking uses hydrochloric acid with a concentration of 0.5-2.0 mol / L.
7. The method according to claim 1, characterized in that, The hierarchical porous carbon material has a three-level hierarchical structure of micropores, mesopores, and macropores, with a specific surface area of 1500 to 2600 m². 2 / g, with a total pore volume of 0.8 to 1.6 cm³. 3 / g, with mesoporous components accounting for 30% to 55%.
8. A hierarchical porous carbon material, characterized in that, The hierarchical porous material is prepared by the method described in any one of claims 1-7.
9. An application of a hierarchical porous carbon material, characterized in that, The hierarchical porous carbon material described in claim 8 can be used in supercapacitor electrodes, electro-deionization adsorption, heavy metal ion adsorption, or catalyst supports.
10. The application according to claim 9, characterized in that, The hierarchical porous carbon material exhibits a specific capacity greater than 320 F / g in a three-electrode system and 6 mol / L KOH electrolyte at a current density of 0.5 A / g, and a capacity retention rate greater than 80% at a high current density of 20 A / g.